This invention relates to the threading of a travelling web strip through process machinery incorporating rotating rolls. More specifically, this invention relates to a method and apparatus for automatically threading the so-called "tail" in a papermaking machine from a roll on which the web is applied to its surface, such as a calender roll, downstream to other apparatus, such as a dryer section. Still more particularly, this invention relates to the combination of a doctor operating against the paper tail on the calender roll to urge the tail into proximity with a foil which, in turn, urges the moving tail away from the calender roll and against a knife to sever the tail and simultaneously direct the severed end onto a support plate for conveyance downstream.
In today's papermaking industry, as speeds become faster, safety and operating regulations become more stringent, and the cost of delay in bringing a papermaking machine up to operating speed after a paper break becomes more significant, there has developed a long-felt need for apparatus which can thread the paper web by way of a paper tail, or narrow portion of the web called a strip, automatically from one section of the machine to another. Heretofore, such threading was often accomplished either by hand, where a machine tender would take the strip and guide it in the open space between sections and then toss it into the next section of the machine where it might be nipped between rolls, or handled by some sort of hand held or manually actuated apparatus. Most prior threading techniques involved either manual, semi-manual, or labor intensive apparatus which was not reliable and seldom operable completely from a benchboard so as to satisfy today's employer safety rules.
Other prior apparatus for guiding a travelling strip of paper from one section to another in a papermaking machine are disclosed in U.S. Pat. Nos. 4,179,330 and 4,501,643.
Prior web threading apparatus, while often utilizing such considerations of web guidance and conveyance as the Coanda effect and the use of a cushion of air over a support plate, have not provided the degree of automatic web threading desired and required in some operational configurations of papermaking machinery. In addition, prior web threading apparatus often required human assistance in manipulating the apparatus to "automatically" thread the machine. Even then, often the tail would be directed into the downstream apparatus upon rethreading the machine where it would sometimes accumulate within the machinery, or slacken, before the tail could be expanded to the full width web for continuous operation. Finally, prior arrangements did not combine automatic benchboard controlled threading with the step of severing the web strip.